i want to allow player to make a 1st hero as normal, but in order to make the 2nd hero, one should have:
- armor researched to level 3
- weapons dmg researched to lvl 3
- submerged researched
- 6 x coral beds buildings (coral beds are the supply depots of naga)

each hero have a group of fields that say techtree requirements tier 2, 3 and some more. there is also a tiers used field. if you have 2 heroes you need to set tiers used to 2 and place the requirements you want in the tier 2 field. you also need a trigger to limit heroes to 1. you will need some more triggers as well. as you want 2 level 3 and 1 level 1 upgrade you need add a custom upgrade that you activate through a trigger. (as you can only specify required levels for all required technologies. meaning that they all have to be same level for it to work.) i could help you create it tomorrow if you want.